1. Technical Field
The present invention relates to a virtual image display device such as a head-mounted display that is used by being mounted on the head.
2. Related Art
In recent years, as a virtual image display device that allows a virtual image to be formed and to be observed similarly to the head-mounted display, various virtual image display devices of a type in which image light from a display element is guided to a pupil of an observer by a light guiding plate have been suggested.
In this virtual image display device, the image light and external light overlap with each other, such that a see-through optical system has been suggested (refer to JP-A-2006-3879 and JP-A-2010-224473).
However, in the device disclosed in JP-A-2006-3879 or the like, the see-through is realized by a pupil division method that uses a light guiding optical system in which an emission opening is smaller than a pupil size, such that it is difficult to make a display size of the virtual image large. In addition, the light guiding optical system that is smaller than the size of the pupil is used, such that it is difficult to make an effective pupil diameter (a lighting diameter that allows the virtual image to be taken in, and is called an Eyring diameter) large so as to correspond to an individual pupil width in human beings. In addition, the emission opening or a casing of the light guiding optical system is physically disposed in the vicinity of the pupil, such that a blind spot is generated, and therefore it is not necessarily a perfect see-through.
In addition, as an optical system for the head-mounted display, an optical system including a light guiding pipe that allows a plurality of light modes in which the light guiding angles are different from each other to progress (refer to JP-A-2008-535001) is disclosed. In this optical system, it may be considered that a third optical surface at an emission side is set as a half mirror, and light that is transmitted through the third optical surface is made to go straight to realize a see-through type display device.
However, in the optical system disclosed in JP-A-2008-535001, a liquid crystal panel is illuminated with collimated light in which a different angle of incidence is set for each of the optical modes on the assumption that a phase of each of the plurality of optical modes is misaligned. In addition, display content is changed by each optical mode, and a display of each optical mode is sequentially performed, and thereby an image of each optical mode is connected to obtain an entire image. In this case, a center image and left and right images, which make up the entire image, are necessary to be displayed while these are changed at a time difference by one liquid crystal panel, such that a virtual image display device becomes complex and an observed image becomes dark.
Separately from this configuration, it may be considered that a virtual image display device that allows a virtual image to be observed in an overlapped manner with external light by a light guiding member provided with a light emitting portion to cover the front of an eye, in which it is not necessary to connect an image at a time difference. However, it is difficult to display a large image, and in a case where a member such as a see-through prism is connected to the light guiding member, ghost light is generated due to this member and therefore the ghost light easily reaches an eye.